This invention lies in the field of processes for thermoforming hollow multilayered plastic articles from a sheet of thermoplastic material.
Many processes have been advanced for manufacturing a hollow plastic article formed of a plurality of layers wherein the article is provided with an inner wall of a plastic material having certain desired properties and an outer wall of a plastic material exhibiting other desired properties. For examples, Berger U.S. Pat. No. 3,122,598 discloses a process for forming decorative plastic articles using injection molding techniques, Sherman U.S. Pat. No. 2,710,987 discloses a method and apparatus for forming laminated plastic articles using extrusion blow molding techniques, and Valyi U.S. Pat. No. 3,719,735 discloses a process for blow molding a laminated containiner from a composite parison which is formed by injecting a thermoplastic material over a preformed liner.
While thermoforming techniques have been used to form hollow articles utilizing preformed laminated sheets comprised of one or more layers of plastic materials, none of such techniques have employed a combination of a preformed thermoplastic sheet and an extruded mass or quantity of a different thermoplastic material deposited thereagainst.
Multilayered plastic containers offer various advantages, substantial resistance to oxygen permeation, resistance to carbon-dioxide duffusion, capacity for storing products under moderate pressure over extended period of time, and the like.
In one prior art plastic sheet thermoforming technique, a fluid pressure applied within a pressure box, such as a pressure produced by compressed air or the like, presses a softened plastic sheet material against the contours of a male mold while a relatively low pressure is exerted from the male mold. In another prior art plastic sheet thermoforming technique, a vacuum from with a female mold is exerted upon one face of a softened plastic sheet material while atmospheric pressure (or a pressurized fluid) is exerted upon the opposing face thereof a shape such softened thermoplastic sheet material against the surface of a female mold. It is possible to use a combination of these two techniques.